Capacitive sensor technology has proven to be a reliable measurement technology that is suitable for demanding environments. Capacitive sensors are used in many applications, such as industrial, automotive, medical and consumer applications.
Sometimes, capacitive sensors are used for distance measurement and position detection. A changing electric field is created between at least two electrodes and the corresponding displacement current or shift current is measured. The capacitance or capacitive coupling network between electrodes is calculated via the relationship between voltage and current. An object brought into the electric field changes the dielectric between the electrodes and the measurement in at least one of three ways. The object may change the permittivity, the electrical conductance and/or surge part of the electric field to ground.
Using multiple electrodes, an electrical tomography of the space between electrodes can be produced. In larger rooms, the distance between electrodes and the length of the wires or connection lines to front-end electronics increases such that the connection lines emit electrical fields and/or act as antennas to pick up electromagnetic interference (EMI). Sometimes, the connection lines are shielded to prevent emitting electrical fields and acting as antennas. However, shielding increases load capacitances to the voltage driver that builds up voltages between electrodes. The increased load capacitance limits transmit frequency and increases the field independent part of the displacement currents, which reduces sensitivity of the measurement system. On the receiver side, the parasitic input capacitance may be much higher than the capacitance to be measured, which leads to a strong attenuation (capacitive divider) and reduces resolution.
For these and other reasons, there is a need for the present invention.